In the field of the isothermal containers for transporting thermally perishable products the length of preservation of the product to be transported in the desired range of temperatures is a function of the following parameters:
1. Initial temperature of the product to be transported. In the production centres the product is usually stored in cold-storage rooms regulated at known, constant temperatures.
2. Mass and thermal capacity of the product to be transported. The greater the mass and the thermal capacity of the product to be transported, the lower the increase in temperature of the product under the same other conditions.
3. Outside shape of the container. Such shape determines both the surface of the container exposed to the environment, then the thermal exchange, and the outside total thermal exchange factor that, once the environment is determined, is a function of surface finishing, colour of the same, positioning of the surface with respect to the environment.
4. Thickness of the container walls. The larger the thickness of the container walls, the lower the thermal exchange factor relative to the thermal conduction established in the container walls.
5. Environment temperature. The higher the environment temperature, the greater the heat amount exchanged with the product contained in the container and the greater the increase in temperature of the product.
It is self-evident that, once the initial temperature of the product to be transported is determined, the length of conservation of the product to be transported in the desired range of temperatures is also determined by parameters 1, 2, 3, 4 and 5 described above. Such length is extremely limited in the today commercial applications since the materials used for making the containers are characterized by a thermal conductivity which permits a thermal exchange between environment and product to be transported such as to allow a length of conservation of the product to be transported within the desired range of temperatures equal to few hours, usually 1-2 hours.
In case of containers of the returnable type, such length can be prolonged by using refrigerating plates having a lower temperature than the desired temperature inside the container. The most used type of such plates consists of boxes made of polyethylene and filled with water solutions of ethylene or propylene glycol or other chemicals. Such containers are cooled inside cold-storage rooms or refrigerators and then positioned inside the isothermal containers mentioned above. Such refrigerated plates allow a length of conservation of the product to be transported within the desired range of temperatures equal to a few hours, usually 2-4 hours.
Of course, it is possible to use such solution only when the utilized isothermal container may be used again several times as the cost of the above-mentioned refrigerating plates is such as to make their recovery and reuse absolutely necessary. Such solution cannot be conveniently used in case the isothermal containers are of the disposable type, i.e. one-use containers, as in case of isothermal containers made of polystyrene. In the latter case, it is absolutely necessary to use a cold accumulation device which is not only technically effective but also of limited cost such as to make it possible to use such solution also from the economical point of view.
Furthermore, the use of such refrigerating plates causes not negligible problems. Before being used the empty container is usually stored in a suitable store which is under standard environmental conditions depending on the season during which such containers are used. Such environmental conditions can vary in the following ranges:
temperature: 20xc2x0/30xc2x0 C.
relative humidity: 50/80%
The air of the environment under such conditions fills initially also the isothermal container.
When the product to be transported, which is taken out of the cold-storage rooms (such rooms being characterized by temperatures varying between xe2x88x9218xc2x0 C. and 0-5xc2x0 C.), is put into the isothermal container, the temperature of the air within the container decreases to a temperature near that of the product to be transported or the refrigerating plates located inside the container. This causes the relative humidity to increase till 100% so that such humidity begins to condense on the product to be transported, thus causing nearly always damages to the product or not negligible troubles.
The present invention relates to a solution solving the following problems:
prolongation of the length of preservation of thermally perishable products transported by means of isothermal containers of the disposable or returnable type;
control of the relative humidity inside the containers in order to avoid the condensation of the humidity on the transported products.
The solution provided by the invention solves particularly the problems relating to the transportation of thermally perishable products at temperatures higher than xe2x88x9218xc2x0 C. In fact, for transportation at temperatures lower than xe2x88x9218xc2x0 C. the solution already exists for a long time and consists of positioning a determined amount of dry ice (solid carbon dioxide) inside the isothermal container. The positioning inside the isothermal container is done quite at random. Dry ice has a balance temperature of xe2x88x9278.5xc2x0 C. at atmospheric pressure and exchanges heat with the air inside the container and cools such air to temperatures lower than about xe2x88x9218xc2x0 C. Such temperatures are exactly determined by a variety of factors such as the amount of dry ice used, the volume, the shape and the weight of the transported product, and the total thermal exchange factor of the thermal container used.
Such a method cannot be used for the transportation of thermally perishable products that need temperatures higher than xe2x88x9218xc2x0 C. (such as fresh foodstuffs, drugs, etc.) In fact the use of dry ice and the presently used isothermal containers determines temperatures inside the container which are lower than xe2x88x9218xc2x0 C., i.e. not consistent with the market requirements.
The present invention seeks to solve such problem by using a particular type of container. The solution consists of a container provided with partitions capable of forming suitably positioned compartments in which dry ice or other coolants can be placed.
Such partitions can be positioned differently according to requirements. To this end, they can engage to recesses formed in the side walls and in the bottom of the container.
A better understanding of the invention will result by referring to the accompanying drawings that show some containers according to the invention only by way of a not limiting example.